Various designs and solutions have been provided in the past for sensing and immediately analyzing various types of conditions in different environments that otherwise are not easily detectable and measurable without the assistance of some sort of instrumentation. For example, U.S. Pat. No. 4,736,620 to N. Adolph discloses an instrument for continuously measuring knock in internal combustion engines. The instrument is generally made up of a magneto-strictive wire element anchored at one end to the engine and at the other end to a suitable securing means. A permanent magnet/output coil sensing means is provided about the element between its ends and provides a signal indicative of the changes in the element as the result of engine knock. U.S. Pat. No. 4,751,690 to H. A. Krueger discloses a light-conditioned and optic-fiber interferometric hydrophone arrangement for detecting an acoustic field. The arrangement is generally made up of a one piece rigid support shell having along its length a series of opposed and reversely oriented acoustic windows. Each window is provided with a diaphragm. An acoustically responsive bendable beam extends through all windows including the diaphragms arranged therein. A pair of optical fibers extend the length of the beam such that the fibers are disposed on opposed major face sides of the beam. The pair of fibers are also reversely disposed at each window with one fiber being on the front side of the beam at one window and on the back side thereof at the adjoining window all for the purpose of substantially eliminating lateral effects in interferometric analyzing any acoustic field detected by the fibers during arrangement use. U.S. Pat. No. 4,841,778 to M. A. Butler et al. relates to a laser-conditioned optical fiber arrangement for use in an electrolytic cell for detecting optical fiber strain variations and thus changes in electro-chemical deposition. The arrangement is generally made up of a pair of optical fibers both being threaded through an electrolytic cell with one being a working electrode and subject to electro-deposition during cell use. As the deposition varies, the strain on the electrode fiber varies and with the other fiber being a reference fiber, the difference in optical path lengths between the two fibers can be detected by interferometry techniques. However, none of the aforediscussed patents whether taken singly or in any combination remotely suggest the improved passive and laser-conditioned magnetic field sensor of the instant invention where the sensor is of integrated and compact construction and incorporates a novel magnetic field sensing and indicating device. This device is generally made up of a nonmagnetic substrate, magneto-strictive ribbon-like material (MSM) and a multistrand optic fiber element of generally serpentine shape and generally flat planar profile. The number of strands per element depends upon its application and use. During manufacture, the optic fiber element is connected to the MSM and then both the connected MSM and the element are selectively tensioned prior to being affixed as tensioned to the substrate. This enables the MSM that is not only responsive to a magnetic field being detected but also maintains sufficient tensioning of the optic-fiber element, despite elongation of the MSM and corresponding decrease in elongation of the element. This sufficient tensioning (pretensioning) of the opto-fiber element despite MSM elongation assures accurate detection of the phase shift in the laser beam transmitted therethrough as effected by the sensor sensor during its use.